President Obama, Michelle Obama, former President Jimmy Carter and former President Bill Clinton arrive ahead of Obama's speech. / Jewel Samad, AFP/Getty Images

by Susan Page, USA TODAY

by Susan Page, USA TODAY

WASHINGTON - The history of modern American race relations was displayed on the steps of the Lincoln Memorial Wednesday.

At the 50th-year commemoration of the March on Washington, the featured finale was delivered by President Obama - as the nation's first African-American president an embodiment of the dream Martin Luther King Jr. had extolled on that same spot a half-century earlier.

"Because they marched, city councils changed and state legislatures changed and Congress changed and, yes, eventually the White House changed," Obama declared to cheers and applause, one of the only personal references he made in his address. "America changed for you and for me."

Also on the scene were two former presidents, each with his own ties to King and debts to the movement he led. The speeches by Bill Clinton and Jimmy Carter that preceded Obama's were testimony to the impact King had on generations of white politicians as well as black ones, and they underscored the repercussions of the civil rights movement in American politics to this day.

"I think most people know that it's highly unlikely that any of us three over on my right would have served in the White House or be on this platform had it not been for Martin Luther King Jr. and his movement, his crusade for civil rights," Carter, 88, said. "So we're grateful to him for us being here."

Carter was born in the 1920s, Clinton in the 1940s, Obama in the 1960s - each growing up in a different era when it comes to race relations.

When he succeeded the race-baiting Lester Maddox as governor of Georgia in 1971, Carter ordered King's portrait hung in the state Capitol and defended him to a skeptical convention of Georgia lawyers and judges in a speech that gained him national attention. He was the first in a wave of "New South" politicians who tried to move beyond the racial divisions of the past, and the first Southern candidate to win the presidency (without first succeeding to it by assassination) since the Civil War.

As for Clinton, he recalled listening to the speakers at the March on Washington from Little Rock, where he was a high school senior. "They opened minds, they melted hearts, and they moved millions - including a 17-year-old boy watching alone in his home in Arkansas," Clinton said from the podium. In his memoirs, he wrote that King's speech, along with his handshake with President John Kennedy at Boys Nation a few months later, became the key moments that propelled him into politics.

Obama, who was a toddler in Hawaii during the march in 1963, hardly needed to reflect on the meaning of the civil rights movement to him personally, given the historic nature of his election in 2008. In a speech that stretched for nearly a half-hour, almost twice as long as King's original address, the president praised the nation's progress over the past half-century but pressed a political agenda of what remained to be done.

"The arc of the moral universe may bend toward justice, but it doesn't bend on its own," he said, a reference to a famous quotation that King often used. The president cited in particular stubborn and growing economic disparities. Noting that the original demonstration was titled the March on Washington for Jobs and Freedom, he asked, "For what does it profit a man, Dr. King would ask, to sit at an integrated lunch counter if he can't afford the meal?"

King spoke in the stirring cadences of a preacher, not usually Obama's manner. But in passages recalling the struggles of the civil rights era, Obama spoke with emotion reminiscent of the early speeches that propelled him to the presidency.

(The two living former Republican presidents, George H.W. Bush and George W. Bush, cited health problems in declining invitations to attend.)

In the wake of the civil rights movement and the legislation that followed, both political parties were reshaped - the Republicans winning the allegiance of white Southerners who had long been Democrats, and the Democrats able to count the growing number of black voters as their most loyal supporters.

That allegiance among African-American supporters helped Clinton survive impeachment and enabled Obama to win re-election despite stubbornly high unemployment - although the racial divide in American politics is presumably not exactly what King had in mind, that afternoon in 1963.